Optical fiber connector tuning index tool

ABSTRACT

A tuning index tool for use in determining the degree of tuning necessary for a tunable optical fiber connector has a first stationary member having a connector adapter affixed thereto and a second movable member within the first member and spring loaded with respect thereto. The second member has a connector adapter affixed thereto axially aligned with the adapter in the first member. The movable member is incrementally rotatable with respect to the stationary member by being pulled against the spring force to disengage the ferrules of connectors in the adapters, which are aligned in a split sleeve. Rotation changes the orientation of the eccentricity vectors of the two connectors, and hence the insertion loss. Measurements of insertion loss are made, and the orientation of the connectors for minimum loss is noted. The number of incremental rotations of the tool indicates the incremental rotation of the ferrule of the connector under test, the eccentricity vector orientation of the other connector being known, that is necessary to achieve minimum insertion loss for the connector with connectors have a known eccentricity vector orientation.

RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.09/363,906 and Ser. No. 09/362,203, both filed concurrently herewith.

FIELD OF THE INVENTION

This invention relates to an optical fiber connector indexable tuningtool and, more particularly to a tool for testing an calibrating tunableoptical fiber connector and apparatus for tuning it.

BACKGROUND OF THE INVENTION

In optical fiber communications, connectors for joining fiber segmentsat their ends, or for connecting optical fiber cables to active orpassive devices, are an essential component of virtually any opticalfiber system. The connector or connectors, in joining fiber ends, forexample, has, as its primary function, the maintenance of the ends in abutting relationship such that the core of one of the fibers is axiallyaligned with the core of the other fiber so as to maximize lighttransmissions from one fiber to the other. Another goal is to minimizeback reflections. Such alignment is extremely difficult to achieve,which is understandable when it is recognized that the mode fielddiameter of, for example, a single mode fiber is approximately nine (9)microns (0.009 mm). Good alignment (low insertion loss) of the fiberends is a function of the alignment, the width of the gap (if any)between the fiber ends, and the surface condition of the fiber ends, allof which, in turn, are inherent in the particular connector design. Theconnector must also provide stability and junction protection and thusit must minimize thermal and mechanical movement effects.

In the present day state of the art, there are numerous, different,connector designs in use for achieving low insertion loss and stability.In most of these designs, a pair of ferrules (one in each connector),each containing an optical fiber end, are butted together end to end andlight travels across the junction. Zero insertion loss requires that thefibers in the ferrules be exactly aligned, a condition that, given thenecessity of manufacturing tolerances and cost considerations, isvirtually impossible to achieve, except by fortuitous accident. As aconsequence, most connectors are designed to achieve a useful,preferably predictable, degree of alignment, some misalignment beingacceptable.

Alignment variations between a pair of connectors are the result of theoffset of the fiber core centerline from the ferrule centerline. Thisoffset, which generally varies from connector to connector, is known as“eccentricity”, and is defined as the distance between the longitudinalcentroidal axis of the ferrule at the end face thereof and thecentroidal axis of the optical fiber core held within the ferrulepassage and is made up of three vectors. It is often the case,generally, that the ferrule passage is not concentric with the outercylindrical surface of the ferrule (vector I), which is the referencesurface. Also, the optical fiber may not be centered within the ferrulepassage (vector II whose magnitude is the diametrical difference dividedby two) and, also, the fiber core may not be concentric with the outersurface of the fiber (vector III). Hence eccentricity can be the resultof any one or all of the foregoing. The resultant eccentricity vectorhas two components, magnitude and direction. Where two connectors areinterconnected, rotation of one of them will, where eccentricity ispresent, change the relative position of the fibers, with a consequentincrease or decrease in the insertion loss of the connections. Where themagnitude of the eccentricities are approximately equal the directioncomponent is governing, and relative rotation of the connectors untilalignment is achieved will produce maximum coupling.

There are numerous arrangements in the prior art for “tuning” aconnector, generally by rotation of its ferrule, to achieve an optimumdirection of its eccentricity. One such arrangement is shown in U.S.Pat. No. 5,481,634 of Anderson et al., wherein the ferrule is heldwithin a base member which maybe rotated to any of four rotational oreccentricity angular positions. In U.S. Pat. No. 4,738,507 of Palmquistthere is shown a different arrangement and method for positioning twoconnectors relative to each other for minimum insertion loss or maximumcoupling. The arrangements of these patents are examples of the effortsto achieve optimum reliable coupling, there being numerous otherarrangements and methods.

In all such arrangements for achieving optimum coupling with connectorshaving different magnitudes and directions of eccentricities, the tuningtakes place, usually, if not always prior to the final assembly of theconnector. As a consequence, an installer in the field has no controlover the degree of coupling, other than by trial and error. Further,tuning of the connector cannot be performed after production of theconnector is completed. Thus tuning prior to final assembly of theconductor is a step in the production process.

An optical fiber connector that can be tuned for optimum performanceafter the connector has been assembled would greatly decrease productioncosts and further, impart a greater measure of reliability to theconnectors. Such a connector would be of significant commercial value.

SUMMARY OF THE INVENTION

The present invention is a tuning index tool for use in tuning tunableoptical fiber connections for achieving maximum possible signaltransmissivity or minimum insertion loss despite the connector beingfully assembled. In a preferred embodiment of the invention theprinciples thereof are illustrated with a connector of the LC type forsingle mode fibers. It is to be understood that the principles of theinvention are applicable to numerous other types of connectors such as,for example, the SC, FC and ST type connectors, as well as to otherfiber optic type devices.

A connector for which the present invention is used is, for purposes ofillustration, is a modified LC type connector, as shown in U.S. patentapplication Ser. No. 09/363,906. The basic components of such aconnector as shown in that patent application comprise a ferrule-barrelassembly for holding the end of an optical fiber extending axiallytherethrough and a plug housing member which contains the barrel-ferruleassembly. A coil spring member contained within the housing surroundsthe barrel and bears against an interior wall of the housing and anenlarged barrel member, thereby supplying forward bias to thebarrel-ferrule assembly relative to the housing. The barrel member,referred to as a flange in the Anderson et al. patent, is shaped to besupported within an interior cavity within the housing in any one offour rotational orientations with respect to the central axis of thefiber holding structure. A ferrule extends axially from the enlargedbarrel member and contains a fiber end therein. Thus the direction ofeccentricity of the fiber relative to the central axis can have any oneof four rotational or angular orientations. The connector is “tuned” tothe extent that four orientations are possible. However, the “tuning” isa manufacturing step preceding final assembly of the connector, afterwhich it is no longer “tunable”.

The ferrule-barrel assembly of the connector is modified so that theenlarged barrel member or flange is optimally hexagonal in shape, andhas a tapered or chamfered leading surface which may be slotted. Thehousing is also modified so that the interior cavity is hexagonal inshape to accommodate the barrel member in any of six rotationalorientations and a sloped constriction against which the leading surfacebears in its forward position. Tuning of the fully assembled connectoris accomplished by the application of an axial force to the barrelmember, as by a spanner wrench fitted within the slots in the leadingsurface, sufficient to overcome the bias of the coil spring and to pushthe barrel portion rearwardly out of engagement with the hexagonallyshaped recess in the housing and the sloped constriction. Theferrule-barrel assembly is then incrementably rotatable to any of sixangular orientations, sixty degrees (60°) apart. It should be noted thata lesser number of surfaces can be used if the diagonal distance of thebarrel cross-section is reduced sufficiently to allow rotation thereofwithin the plug housing or, alternatively if the housing bore isenlarged, which, however, weakens the walls of the housing. Fewersurfaces means larger increments of rotation and hence less precisereduction in loss. Also, more than six surfaces may be used, however,the improvement over six surfaces is slight and the clearancesurrounding the barrel makes limiting rotation within the housingdifficult to achieve.

In accordance with the invention, an indexable tuning tool having aspring loaded split LC adapter that is keyed and labeled to measure theoptical performance of an LC connector at six different angularorientations. The tool has a longitudinal split ceramic sleeve thereinfor aligning two LC connector end faces. In operation, a test jumpercable having an LC connector which has an eccentricity of a magnitudegreater than that of the connector to be tuned and a known direction(angular orientation), is inserted into the sleeve and the productionjumper connector is fitted into the sleeve so that the connector ferruleends abut. The opposite end of the jumper cable is connected to anoptical source, or an optical detector, and the production jumper isconnected to a source or detector to complete a test circuit. Ideally,the test jumper has an eccentricity of 1.8 to 3.5 μm relative to theferrule axis, and has an angular orientation of zero degrees (0°) or onehundred eighty degrees (180°), preferably the former which is an uprightvertical orientation. Insertion loss measurements are then taken and theinitial loss is noted. The portion of the tool holding the productjumper is spring loaded to allow separation of the fiber end faces androtation thereof. The tool is thus rotated in sixty degree (60°)increments, with measured insertion loss being recorded at eachincrement. The angular orientation of the product jumper that yieldsminimum insertion loss is thus determined. The labeling on the toolindicates how many degrees, in sixty degree increments, the productjumper had to be rotated to produce minimum insertion loss. Inasmuch asthe angular orientation of the connector of the test jumper is known,preferably, as stated hereinbefore, zero degrees (0°) or straight up orvertical, the tool indicates how many incremental stages the productjumper requires to have a corresponding vertical orientation. It is alsofeasible to ascertain, instead of minimum insertion loss, the angularorientation for maximum insertion loss. Rotation of 180° from thisorientation yields the orientation for minimum insertion loss. In bothmethods, one or the other of the extremes of insertion loss isdetermined.

A tool, used for tuning, in the form of a spanner wrench is included asan element of the tuning test operation. The tuning tool wrenchcomprises an enlarged handle shaped, such as hexagonally, for grippingfrom which extends a hollow sleeve having a distal end with first andsecond tangs extending therefrom. The sleeve is adapted and sized to fitover the ferrule of the product jumper connector with the tangs engagingthe slots in the leading or front surface of the barrel member. In use,the tangs are engaged and the ferrule-barrel assembly is pushed to therear out of engagement with the plug housing and against the springbias, so that the ferrule-barrel assembly may be rotated the requirednumber of degrees as indicated by the index tool to the angularorientation yielding minimum insertion loss where the connector is matedwith another connector having vertical orientation of its eccentricity.The spanner wrench of the invention has a shoulder from which the sleeveextends, which butts against the housing to limit the insertion distanceof the wrench. The distance from the face of the shoulder to the tangsis chosen such that the ferrule-barrel assembly, when pushed against thecoil spring, does not cause the spring to bottom, which can be damagingto the spring. The barrel is then rotated to the tuned position. Whenthe wrench is removed, the spring returns the barrel forward to its newrotated position. In this manner, the product connector is tuned. It iscontemplated that all mating connections will have such a verticalorientation, hence the installer, for example, does not have to beconcerned with optimum tuning.

Thus the unique structure of the connector permits tuning of theassembled connector. Further, the tuning tool enables additionalrotations of the ferrule-barrel assembly when desired, for whateverreason, such as where it is desired to have operation at a predeterminedvalue of loss, as when channel balance among several channels isdesired.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of the components of theconnector;

FIG. 2 is a perspective view of the assembled connector;

FIG. 3a is a front elevation view of the connector housing, frontportion;

FIG. 3b is a cross-sectional side elevation view of the front portion;

FIG. 3c is a front elevation view of the connector housing firstportion, adapted to receive the ferrule-barrel assembly of FIGS. 4c and4 d;

FIG. 4a is a side view of a modified ferrule-barrel member of theconnector;

FIG. 4b is a front elevation view of the member of FIG. 4a;

FIG. 4c is a side elevation view of a modification of the ferrule-barrelassembly of FIG. 1 or FIG. 4a;

FIG. 4d is a front elevation view of the assembly of FIG. 4c;

FIG. 5a is a side elevation cross-sectional view of the connector;

FIG. 5b is a side elevation cross-sectional view of the connector in itstuning configuration;

FIG. 6 is a graph of the effect of offset between two fiber ends;

FIG. 7 is a bar chart of the distribution of insertion loss for untunedconnectors;

FIG. 8 is a bar chart of the distribution of insertion loss for tunedconnectors;

FIG. 9 is an exploded perspective view of a tuning index tool;

FIG. 10 is a side view of the test tool of FIG. 9 as assembled;

FIG. 11 is a cross-sectional view of the tool along the lines A—A ofFIG. 10;

FIG. 12 is a perspective view of the assembled tool;

FIG. 13 is a perspective view of the tuning index tool of FIG. 10 asused in performing tuning tests;

FIG. 14a is a perspective view of the tuning wrench of the invention fortuning a connector;

FIG. 14b is a front elevation view of the wrench of FIG. 14a;

FIG. 14c is a cross-sectional view of the wrench of FIG. 14b along theline B—B;

FIG. 14d is a cross-sectional view of the wrench of FIG. 14b along theline A—A;

FIG. 14e is a detail of the tuning operation using the wrench of FIG.14b; and

FIG. 14f is a cross-sectional view of the connector of the invention asit is being tuned by the wrench.

DETAILED DESCRIPTION

FIG. 1 is an exploded perspective view of the principal components of anLC type connector 11 which embodies the principles of the presentinvention. It is to be understood that these principles are alsoapplicable to other types of connectors, such as an ST, SC, or otheramenable to modification to incorporate these principles. Connector 11comprises a plug housing formed of a front section 12 and a rear section13 having an extended portion 14 which fits into section 12 and latchesthereto by means of slots 16—16 in front section 12 and latching members17—17. Members 12 and 13 are preferably made of a suitable plasticmaterial. Member or front section 12 has a resilient latching arm 18extending therefrom for latching the connector 11 in place is areceptacle or adapter. Member or section 13 has extending therefrom aresilient latch arm or trigger guard 19, the distal end of which, whenthe two sections 12 and 13 are assembled, overlies the distal end of arm18 to protect it from snagging and to prevent nearby cables frombecoming entangled. Usually latch arm 18 and guard 19 are molded withtheir respective housing sections 12 and 13, respectively, and form“living hinges” therewith, which enable them to be moved up and downbetween latching and unlatching positions. Front section 12 has a bore21 extending therethrough which, when the parts are assembled, iscoextensive with a bore 22 extending through rear section 13. The bores21 and 22 accommodate a ferrule-barrel assembly 23 which comprises ahollow tubular member 24 having an enlarged flange or barrel member 26from which extends a ferrule 27 which may be made of a suitably hardmaterial such as, preferably, ceramic, glass, or metal. Ferrule 27 has abore 28 extending therethrough for receiving and holding an opticalfiber therein. When the connector 11 is assembled, a coil spring 29surrounds the tubular portion 24 of the assembly 23, with one endbearing against the rear surface of flange 26 and the other end bearingagainst an interior shoulder in rear section 13, as will best be seen insubsequent figures.

In practice, the uncoated portion of the optical fiber is inserted intobore 28 of ferrule 27 and adhesively attached thereto. Spring 29 iscompressed as the sections 12 and 13 are connected and supplies aforward bias against the rear of flange 26 and, hence, to ferrule 27.This arrangement of ferrule 27 and spring 29 is considered to be a“floating” design. Prior to connection, the spring 29 causes ferrule 27to overtravel its ultimate connected position. When connector 11 isconnected within a suitable adapter and the distal end of ferrule 27butts against the corresponding ferrule end of another connector or ofother apparatus, spring 29 will be compressed, thereby allowing backwardmovement of ferrule 27 to where its end, and the end of the abuttingferrule, lie in the optical plane (transverse centerline) between thetwo connectors.

The rear end of rear section 13 has a ridged member 31 extendingtherefrom for attachment of optical fiber cable and a strain reliefboot, not shown. For protection of the distal end of ferrule 27 duringhandling and shipping, a protective plug 32, sized to fit within bore21, is provided. FIG. 2 depicts the assembled connector 11 in itsshipping or handling configuration.

As best seen in FIGS. 4a and 4 b, flange 26 has a hexagonally shapedportion 33 and a front tapered portion 34, which can be a taperedextension of the hexagon shape. While the following discussion relatesto a multi-faceted ferrule holding member, it is to be understood thatthe term “faceted” is intended to include other locating arrangementssuch as, for example, sots or splines. Front section 12 has a flangeseating opening 36 formed in a transverse wall 37 thereof which has ahexagonally shaped portion 38 and a tapered portion 39 dimensioned toreceive and seat flange 26, as best seen in FIGS. 3a and 3 b. In FIG.3c, the opening 36 has, instead of a hexagonal shape, a plurality ofsplines 40 extending inwardly therefrom, a modification especiallyadapted to receive the ferrule-barrel assembly of FIGS. 4c and 4 d. Thatportion 41 of bore 21 immediately to the rear of portion 38 has adiameter sufficient to allow rotation of flange 26 when it is pushed tothe rear and disengaged from the seat 36. Thus, as will be discussedmore filly hereinafter, when flange 26 is pushed to the rear (againstthe force of spring 29) it may be rotated and, when released, re-seatedwith tapered portion 34 acting as a guide. The hexagonal configurationmakes it possible to seat the flange 26 in any of six angular rotationalpositions, each sixty degrees (60°) apart. It has been found that aflange having fewer than six sides cannot be rotated in the assembledconnector unless the diameter of bore portion 41 is increased becausethe diagonal of a four sided flange is too great for rotation of theflange. However, increasing the diameter of portion 41 seriously weakensthe walls of the housing section 12. Further, in the tuning of theconnector it has been found that six sides gives a more accurate tuningfor reduction of insertion loss. The use of a flange with more than sixsides is possible, and gives an even greater tuning accuracy by creatingsmaller increments of rotation. However, the increased accuracy is notsufficiently great to justify the increased difficulty in achieving astable and firm seating of the flange. As the number of flange sides isincreased, the periphery thereof approaches a circular configuration,which would not be seated firmly and which possibly would be rotatableeven when seated. As a consequence, it has been found that a six sidedflange is optimum.

FIGS. 4a and 4 b show a modification of a barrel-ferrule assembly 23 inwhich the sloped or tapered portion 34 has a notch 42 therein foraccommodating a tuning tool, not shown.

FIGS. 5a and 5 b depict, in cross-section, the connector 11 of thepresent invention showing, in FIG. 5a, the flange seated position and inFIG. 5b, the disengaged and rotatable position of the flange for tuning,demonstrating how tuning is achievable with a fully assembled connector.It should be noted that the thickness of the wall 37 is slightly lessthan that of flange 26, thereby insuring that flange 26 can bedisengaged (pushed back) from the seat 36 to where it can be rotatedwithout causing spring 29 to bottom. Connector 11 is shown mounted onthe end of a cable 43 containing a fiber 44, which extend throughconnector 11 as shown.

FIG. 6 is a graph of the effect of offset between two fiber ends (twoconnectors) which is “transverse offset” versus attenuation. For verysmall offsets, such as 0.5 microns (point Y), the loss is correspondingsmall, about 0.05 dB. In the range from zero offset to one micron (POINTY′), the loss remains well below 0.3 dB, which is a preferred limit onloss. The next increment range of offset, from one micron to two microns(point Y″) shows an exponential increase in loss, from about 0.22 dB to0.9 dB. Thus, it can be seen that for each incremental increase of onemicron offset, the loss increases exponentially. It can be appreciatedtherefore, that tunability of the connector to decrease the offsetbetween the two fiber ends is highly desirable.

FIG. 7 is a bar chart of the measurements on a group of untunedconnectors showing a wide distribution of insertion loss. It can be seenthat several of the connectors exceed the preferred insertion loss limitof 0.3 dB. FIG. 8 is a bar chart of the same group of connectors aftertuning, showing a compression of the loss distribution to where only oneconnector exceeds the 0.3 dB limit. Thus, from FIGS. 7 and 8, it can beseen that tuning materially enhances the performance of connectors wherethere are eccentricities present, which is virtually always the case.

Tuning Index Tool

FIG. 9 is an exploded perspective view of the tuning index tool 51 ofthe invention discussed hereinbefore. Tool 51 comprises housingcomprising a hollow circular member 52, preferably of a plasticmaterial, having a retaining wall 53 for a warped leaf spring 54. Member52 has a plurality of openings or windows 56 around the peripherythereof, spaced sixty degrees (60°) apart, and a plurality of keyways57, only one of which is shown in FIG. 9, which are spaced around theinner periphery of member 52 and spaced preferably one hundred twentydegrees (120°) apart. With reference to FIG. 11, which is across-section of tool 51 along the lines A—A of FIG. 10, member 52 has awall 58 therein, formed by disc member 59 which has a connector adapter61 affixed thereto on one side. Extending from the other side of disc 59is a split sleeve 62, preferably of a ceramic material, held withinadapter 61, for receiving the ferrule of a connector mounted in adapter61. Sleeve 62 also receives the ferrule of a connector mounted in asecond adapter 63 which is affixed to a wall 64 of a movable member 66.Disc member 59 has a circular array of locating holes 67 surrounding alocating ring 68 which seats in a circular groove 69 wall 64 of member66. As best seen in FIG. 11, wall 64 has extending therefrom sixlocating projections 71 which are dimensioned to fit within openings orlocating holes 67. Holes 67 form a circular array, with the holes spacedsixty degrees (60°) apart, and, importantly, with one of the holes beingat zero degrees (0°) relative to the vertical axis of adapter 61. On theother hand, locating projections or pins 71 are in a circular array andspaced sixty degrees (60°) apart, with one projection or pin 71 being atzero degrees (0°) relative to the vertical axis of adapter 63. The outeredge of wall 64 preferably has a locating mark 72 thereon which, as willbe apparent hereinafter, is visible through the windows 56 as member 66is rotated during tests. Preferably locating mark 72 is aligned with thevertical axis of adapter 63 and is, as a consequence, an indicator ofthe zero degree (0°) location of adapter 63. It should be obvious thatsix pins 71 are not absolutely necessary, since the locating feature canbe accomplished with as few as one pin.

Tool 51 is assembled by spring 54 being placed within member 52 to bearagainst retaining wall 53, as seen in FIG. 11. Movable member 66 is theninserted into member 52 so that wall 64 rests against spring 54. Discmember 59, the periphery of which has projecting key 73, is theninserted into member 52 with the key being inserted into keyways 57, andlatched therewithin by a plurality of peripherally disposed latchingmembers 74 on member 59 and latching slots 76 within member 52. Sleeve62 is fitted within the two adapter sleeves, as shown in FIG. 11. Theassembled tool 51 is shown in FIGS. 10 and 12, and the tool in use isshown in FIG. 13.

In use, as best seen in FIG. 13, a test jumper 81 which terminates in anLC connector, not shown, is inserted into adapter 63. The connector hasa known magnitude of offset or eccentricity greater than the connector82 to be tested for tuning oriented vertically (0°). The orientation canbe 180°, which is also vertical, but the following discussion will bedirected toward the 0° orientation. Preferably the magnitude of theeccentricity relative to the ferrule axis is 1.8 to 3.5 microns. Theconnector 82 to be tuned is inserted into adapter 61 and has a unknownamplitude and direction of eccentricity. With marker 72 showing in oneof the windows, such as, for example, the 0° orientation window, whichmay be indicated by a marking strip 83 affixed on the periphery ofmember 52 (see FIG. 12), insertion loss is measured. The operator thenpulls member 66, which is ridged to give purchase, in the directionindicated by arrow A, against spring 54 until the ferrules of the twoconnectors are disengaged and locating pins 71 are cleared from openings67. The member 66 is then rotated, for example, clockwise direction B),until the marker 72 appears in the next window 56, in other words,member 66 is rotated 60°, as is connector 63. Insertion loss is againmeasured and recorded. The process is repeated for five more incrementalrotations, and the measured insertion losses will have a maximum and aminimum. It is noted at which incremental position the insertion losswas the least, for example, it was least at the second rotationalposition, which is an indication that 120° of rotation resulted inclosest alignment of the fiber ends. The connector to be tuned is thenremoved from the tool. Suitable means, such as the especially designedspanner wrench previously discussed, is then used to rotate the ferruleof the connector 120° counter-clockwise in the manner explainedhereinbefore, to “tune” the connector. Inasmuch as the eccentricityvector of the test jumper was vertical (0°) during the test, then theeccentricity vector of the product connector is now also vertical, andthe connector junction with the other “tuned”, or vertically orientedeccentricity, connecting member, will exhibit the minimum achievableinsertion loss for that connection. The foregoing process may bepracticed to determine a degree of loss between the extremes for use inchannel balancing.

Tuning Wrench

As pointed out hereinbefore, after the insertion loss measurements arecompleted and the eccentricity orientation of the connector determined,the product connector must then be tuned to the indicated orientation.The tuning of the connector is discussed in connection with FIGS. 5a and5 b wherein it is shown that the ferrule 27 is pushed into the connectoragainst the force of spring 29 until the flange 26 clears the flangeseating opening 36 sufficiently to allow the ferrule/barrel assembly tobe rotated. This movement of the ferrule may be accomplished by anysuitable means, such as, for example, needle nose pliers which are usedto grip the ferrule and to push it. The ferrule is made of sufficientlyhard material, such as a ceramic, that judicious gripping thereof withpliers is generally insufficient to damage the ferrule. It is desirablethat the ferrule-barrel assembly not be pushed so far that the spring 29bottoms, which can, over time, weaken the spring or even damage it.

In FIGS. 14a through 14 f there are shown several views of a uniquetuning wrench 83 for use with the ferrule-barrel arrangement of FIG. 4a.Wrench 83 has a first, enlarged, body portion 84 having a hexagonalshape for ease of gripping. It is to be understood that portion 84 canhave other shapes besides hexagonal; however, the hexagonal shape makespossible an easy determination of when a 60° rotation has been achieved.Extending from portion 84 is a limiting member 86 having a diametergreater than bore 21 in the front portion of connector 11 and a flatface 87 at its distal end. Extending from face 87 is a strengtheningmember 88 which has a diameter that is less than the bore 21. A centralbore 89 extends through member 84, 86, and 87 as shown. A tubular member91 is located in bore 89 and affixed thereto. Member 91 is preferablymade of metal, although it is not intended that it be restrictedthereto, since other materials may be suitable. The distal end of member91 has first and second tangs 92 and 93, diametrically opposite eachother which form a spanner wrench. The inner diameter of member 91 issuch that it slides easily over the ferrule 27 of the connector 11, andtool 83 may then be pushed forward to where the tangs 92 and 93 engageslot 42 of the flange member 26. It will be obvious to workers in theart that one tang can be used. FIG. 14e depicts this operation justprior to such engagement, and FIG. 14f depicts ferrule 27 in thedisengaged position after tool 83 is pushed forward until face 87 buttsagainst the front of the connector, thereby limiting the distance thatthe ferrule/barrel assembly is pushed against the spring. The distancethat member 91 protrudes from limiting member 86 is sufficient to allowtangs 92 and 93 to engage slot 42, plus a distance after such engagementto incur disengagement of flange member 26, as seen in FIG. 14f, but nomore, face 87 blocking any further rearward movement thereof. Bodyportion 84 preferably has a reference hole 94, located at one of thecusps of the hexagonal shape, and, as seen in FIG. 14b, the plane inwhich the tangs 92 and 93 lie is normal to the vertical centerline ofreference hole 94.

The wrench 83 is primarily intended for use with the tuning index tool51 and is used to make the incremental rotations of the productconnector, the number of increments being indicated by the results ofthe test process discussed hereinbefore. However, the wrench may also beused to make tuning adjustments in the field to the fully assembledproduct connector.

The tuning wrench, as hereindescribed, is the subject of U.S. patentapplication Ser. No. 09/362,203 filed concurrently herewith.

In conclusion of the detailed description, it should be noted that itwill be obvious to those skilled in the art that many variations andmodifications may be made to the preferred embodiment as shown hereinwithout substantial departure from the principles of the presentinvention. All such variations and modifications are intended to beincluded herein as being within the scope of the present invention asset forth in the claims. Further, in the claims hereafter, thecorresponding structures, materials, acts, and equivalents of all meansor step plus function elements are intended to include any structure,material, or acts for performing the functions without specificallyclaimed elements.

What is claimed is:
 1. A tuning index tool for use in tuning anassembled optical fiber connector, said test tool comprising: a hollowmember having a central axis and an open end and a retaining wall at theend thereof opposite said open end, said retaining wall having anopening therein; said hollow member having an interior wall spaced fromsaid retaining wall and having a first connector adapter thereonprotruding toward said open end, said adapter having a first connectorferrule receiving member axially disposed therein; a movable memberwithin said hollow member having an end wall having a second connectoradapter protruding therefrom toward said retaining wall, said adapterhaving a second connector ferrule receiving member axially aligned withsaid first connector ferrule member; and a spring member located betweensaid retaining wall and said end wall for forcing said end wall intocontact with said interior wall of said hollow member, said movablemember being axially rotatable relative to said hollow member when saidend wall and said interior wall are out of contact.
 2. A tuning indextool as claimed in claim 1 wherein a split sleeve member adapted toreceive the ferrules of connectors located in said first and secondadapters is inserted in said first and second adapter connector ferrulereceiving members.
 3. The tuning index tool as claimed in claim 1,further comprising a means for indicating the angular orientation ofsaid movable member to said hollow member.
 4. A tuning index tool asclaimed in claim 1 wherein said hollow member has a circular wall havinga plurality of windows spaced around said circular wall.
 5. A tuningindex tool as claimed in claim 4 wherein said windows are spaced sixtydegrees (60°) apart.
 6. A tuning index tool as claimed in claim 5wherein said end wall of said movable member has a circumferential edgehaving a locating mark thereon, said locating mark being visible throughone of said windows.
 7. A tuning index tool as claimed in claim 1wherein said interior wall comprises a disc member having a circularlocating ring extending therefrom concentric with said central axis. 8.A tuning index tool as claimed in claim 7 wherein said end wall of saidmovable member has a circular axially concentric groove adapted toreceive said locating ring.
 9. A tuning index tool as claimed in claim 7wherein said disc member is insertable within said hollow member and hasa plurality of latching members adapted to latch to matching slots insaid hollow member.
 10. A tuning index tool as claimed in claim 7wherein said hollow member has a circular wall having a plurality ofkeyways therein, sand said disc member has a plurality of keys adaptedto fit within said keyways for locating said disc member within saidhollow member.
 11. A tuning index tool as claimed in claim 1 whereinsaid end wall of said movable member has at least one locating memberprojecting therefrom.
 12. A tuning index tool as claimed in claim 11wherein there is a plurality of locating members projecting from saidend wall in a circular array.
 13. a tuning index tool as claimed inclaim 12 wherein there are six locating members in said circular array,spaced sixty degrees (60°) apart.
 14. A tuning index tool as claimed inclaim 11 wherein said interior wall of said hollow member has aplurality of locating holes therein arranged in a circular array andadapted to receive said locating member.
 15. A tuning index tool asclaimed in claim 14 wherein there are six locating holes in saidcircular array, spaced sixty degrees (60°) apart.
 16. The tuning indextool as claimed in claim 14, wherein the circular array of locatingholes is adapted to receive said locating member in any of a number ofangular orientations.
 17. A method of testing for eccentricityorientation a first optical fiber connector having a ferrule extendingtherefrom comprising: inserting the connector in a tool having a firstadapter for receiving the connector; inserting a test connector in thetool in a second adapter, said test connector having an eccentricityvector of known direction so that the ferrule ends of the two connectorsabut in engagement; measuring the insertion loss; disengaging theferrules and rotating one of the connectors through a first incrementalangle; re-engaging the ferrule ends; measuring the insertion loss;continue the steps of disengaging, rotating re-engaging, and measuringuntil the connector being rotated has rotated through three hundred andsixty (360°) degrees; noting the angular orientation of the connectorsrelative to each other at the stage of minimum measured insertion loss.18. The method as claimed in claim 17 wherein each rotation of theconnector is sixty degrees (60°).
 19. The method as claimed in claim 17wherein the connector being rotated is the test connector.
 20. A toolfor providing selectable insertion loss in optical fiber connections,said tool including: first apparatus comprising a centrally locatedoptical jack and at least a first indexing member; second apparatuscomprising a centrally located optical jack and a plurality of secondindexing members, said first and second apparatuses being shaped toengage each other in a mating relationship; and a spring member adaptedto urge the first and second indexing members into engagement with eachother in one of a plurality of stable rotational positions in a mannerthat allows eccentricity of the optical fiber connection to be measured.21. A tuning index tool comprising: a hollow member having a retainingwall and an interior wall spaced from said retaining wall, said interiorwall having a first connector adapter member; a movable member having anend wall, said end wall having a second connector adapter; and a springmember located between said retaining wall and said end wall for forcingsaid end wall into contact with the interior wall, in which said movablemember is axially rotatable relative to said hollow member when said endwall and said interior wall are out of contact.
 22. A tuning index toolas claimed in claim 21, wherein said movable member has at least oneprojecting locating member and said hollow member has a circular arrayof openings for receiving said locating member in any of a number ofangular orientations.
 23. A tuning tool as claimed in claim 22, whereinthere are six openings in said hollow member spaced sixty degrees (60°)apart.
 24. A tuning tool as claimed in claim 23, wherein there is aplurality of projecting locating members arranged in a circular arrayand spaced equidistant from each other.
 25. A tuning tool as claimed inclaim 24 wherein there are six locating members spaced sixty degrees(60°) apart.
 26. A tuning tool as claimed in claim 22, and furtherincluding means for indicating the angular orientation of said secondmember to said housing.